1. Field of the Invention
This invention relates to hydrophilic-film-forming preparations which form hydrophilic films on surfaces of materials such as metal, glass, plastics, etc.; to articles having such hydrophilic films; and to a method of forming a hydrophilic film especially having corrosion resistance.
The term "article" as herein used means that made of an appropriate industrial material such as metal, glass, plastics etc. in an appropriate shape, for example, a section such as a short-length plate material, a continuous-length plate material (e.g. a rolled product such as foil, sheet, plate), a circular material such as rod, bar, tubular product, a press blank material, an extruded section etc. or workpieces obtained by processing the above into desired final shapes, which have been provided with a film, and in the case of a section, said shape also includes that adaptable for plastic working processes such as forging, deep-forming, bending, punching, etc.
2. Description of the Prior Art
Hydrophilic-film-forming preparations are used for imparting hydrophilic films on material surfaces so as to prevent the formation of condensed water droplets on the material surfaces and also for antistatic and defogging purposes.
For example, in heat exchangers equipped with plate or with corrugated fins, with the progress in the tendency to higher performance and to compactness, the inter-fin distance has been made smaller for improving heat transfer capacity. Heat exchange with the atmosphere is made via the fin surface and atmospheric moisture condenses on the fin surface, but if the inter-fin distance has been made smaller to e.g. 3-4 mm or less, the condensed water forms a bridge between the fins and hence increases the air-flow resistance, thus resulting in noise generation and a reduction in energy consumption efficiency, and therefore, it has been the practice to prevent the bridge formation by imparting hydrophilic properties to the fin surface. For imparting such hydrophilic properties, an appropriate means is employed according to the metal material used, and, for example, it is known to apply resin paints containing a silica powder or a surface active agent as an agent for imparting hydrophilic properties. However, various problems were encountered; for example, the silica powder came off on press molding resulting in reduced uniformity of the film, and in order to avoid this, if the silica powder was added in a large amount, it in turn reduced the thickness of the inorganic film and reduced the corrosion resistance of the film. Whereas, if the hexavalent chrominum ion concentration was increased in order to offset this effect of silica, then the hexavalent ions dissolved out from the formed film and caused die abrasion when die molding was conducted after film formation, or the surface active agent gradually dissolved out with time to decrease the hydrophilic properties, and in some use environments, the increase in hydrophilic properties caused a decrease in the corrosion resistance of the metal material.